To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
Multiple-input-multiple-output technology (abbreviated as MIMO, and also referred to as multi-antenna technology) may exponentially increase spectral efficiency of a wireless communication system by utilizing spatial resources, and therefore has become an important technology of cellular communications. There are many ways of utilizing the multi-antenna technology, among which transmitting diversity is an effective means of using space-time coding to enhance link reliability. Traditional Alamouti code may realize a way of transmitting diversity with Rate=1 in a situation where two antennas are used. Long term evolution (LTE) systems corresponding to an evolved universal terrestrial radio access (E-UTRA) protocol proposed by the third generation partnership project (3GPP) define various ways of transmitting diversity.
A large-scale antenna array (large-scale MIMO, or massive MIMO) system is a main candidate technique of the 5th Generation (5G) cellular communication standards. Large-scale antennas enable a system to use a great number of degrees of freedom of signal processing to dramatically decrease interference among user equipments and interference among cells, and calculation therein is not complex, which may effectively improve the quality of communication links. In addition, the large-scale antennas may effectively reduce power consumption of a single antenna unit, and improve energy efficiency of the overall system. Existing experiments have testified possibility of configuring tens or even hundreds of antennas for a base station. An implementation of large-scale antennas in a millimeter wave band may be that a base station configured with a large-scale antenna array uses phase difference among antennas to form extremely narrow transmitting beams to serve a plurality of user equipments when a distance between the antennas is very small; meanwhile, a user equipment may also be configured with multiple antennas to form different gains for different directions of arrival, and may select a receiving beam with a relatively large gain to receive data. If each transmitting beam of the base station serves one user equipment, then interference among the user equipments will be dramatically reduced; and if two neighboring base stations use transmitting waves in different directions to serve their respective user equipments, then interference among the cells will be dramatically reduced. A theoretic analysis result shows that in a large-scale antenna system, if a transmitter knows accurate channel distribution information (CDI) of channels of a user equipment, then resulting signal-to-noise ratios (SNRs) of downlinks and uplinks may increase as the number of antennas increases; and for tens or even hundreds of transmitting antennas, corresponding system capacities thereof may be improved significantly.
Since it is hard to realize multiple antennas transmitting diversity when there are too many antennas, e.g., a lot of challenges to be encountered with when designing space-time code, currently, LTE systems only define transmitting diversity using four antennas for transmission diversity. Therefore, how to realize transmitting diversity in a large-scale antenna system is a field yet to be exploited.